Orally disintegrating mono-layer tablets are known in the art and widely accepted today in several therapeutic categories. However, there are several practical limitations to these mono-layer orally disintegrating tablets in their manufacturing and storage/handling aspects. For example, these tablets in general are soft and need to be blister-packaged directly off the tablet press. Alternatively, the tablets need to be compressed at very low compression forces, which cannot be used with tablets prepared by direct compression or wet granulation. Additionally, for those orally disintegrating mono-layer tablets containing a coated active, it is important to compress at the lowest force possible, so the coating will not be ruptured under compression. These compression and disintegration issues are further complicated if the orally disintegrating tablet comprises two or more layers where at least one layer is an orally disintegrating layer. One solution may be to use a melt granulation process which allegedly may permit using a compression force as low as 2 kN; direct compression formulations, on the other hand, require compression forces greater than 5 kN.
While such a solution may be acceptable for a monolayer orally disintegrating tablet, such a low compression would not permit a multi-layered tablet having at least one orally disintegrating layer. In the case of a multi-layer tablet, it is imperative that the multiple layers remain attached to each other throughout the shelf-life and use in commerce and that the layers do not separate. Typically, to maintain cohesion of the multiple layers, the tablet must be compressed using a higher force than the force used to compress a monolayer orally disintegrating tablet. Increased compression force results in increased tablet hardness, which, in turn, results in delayed and/or slowed disintegration to unacceptably longer times, i.e., longer than 60 seconds. For example, tablets with hardness greater than 1 kP may not be orally disintegrating, i.e., they may take 1 minute or more to dissolve in the mouth of a subject.
There is a need for a multi-layered tablet that has at least one orally disintegrating layer and that is capable of maintaining layer cohesion throughout storage, transport, and handling.